A multi-beam plotter is a device that uses an array of laser beams to produce an image on a light sensitive media like film or offset plate. In most such machines, the beams in the array are adjacent to one another. In order to receive a good image without artifacts, the intensity of the different laser beams on the exposed media should have a very similar value. Plotters usually have a light calibration system that uses a light detector to calibrate all the laser beams to work at the same intensity. In spite of the light calibration system, the exposed image looks, sometimes, not quite homogeneous. This non-homogeneous exposure can be caused, for example, by a slight difference in the wavelength of the different beams and a non-flat response of the media to the different wavelengths.
In order to solve the non-homogeneity problem, each beam has to be operated separately, its exposure result investigated and the intensity of each diode corrected accordingly. In a multi-beam plotter, exposing with a single beam takes, relatively, a very long time. Hence, This calibration procedure is very tedious and cumbersome.